Manufacture of composite bearings



-Mmh1'1,1941. FET-z' 2,234,371

ANUFACTUR OF COMPOSITE BEARINGS Filed Jine 23, '1938 A'n'oRNEYs PatentedNiar. 11, 1941 MANUFACTURE oF oomosrrn BEARINGS Erich Fetz, Newark, N.J., assigner to Hardy Metallurgical Corporation, New York, N. Y., acorporation of Delaware Application June 23, 193s, serial No. 215,500

a claims. (ci. zii-1495i This invention is concerned with themanufacture of composite bearings-and the like having a layer of bearingmetal'strongly bonded to a mea tallic backing or reenforcing strip andpartic- 5 ularly with the manufacture of composite bearings in which thebearing layer is especially durable. Preferably the bearing layercontains vat least two metals, .for example, copper and lead.

Conventional white metal bearings, for examl ple babbitt, are inadequatein the conditions'of service imposed in modern internal combustionengines and the like. It has been proposed heretofore to substitutecopper-lead alloys for babbitts, etc., in such service and such alloysare l valuable bearing materials because of the relatively low cost oftheir principal constituents and because they combine the advantages ofhigh tensile and compressivestrengths, high thermal conductivity, lowcoefficient of friction and high fatigue strength. However, generaladoption of copper-lead bearings has been hampered heretofore bymanufacturing difficulties, especially in the case' of the so-calledinsert or composite bearings in which a relatively thin layer ofcopper-lead is attached to and backed by a reenforcing member of steelor the like.

The manufacturing difficulties have, been caused, at least in part, bythe lack of mutual solubility of copper and lead in the solid state andthe great difference in specific gravity between the two metals.Although molten copper-lead mixtures containing up to 38% copper arecompletely miscible, nearly pure copper crystals separate from such amolten mixture on passing through the temperature range bounded `by1083,

C. (melting point of copper) and 954 C.` (monotectlc temperature), whileythe remaining lead solidies at 327 C. The liquid phase of nearly purelead tends to coalesce into relatively largey .40 masses duringsolidication and the aggregate 55 lead to. 'steel backings and the like,andV although powders until the netal of lower meltingpoint this may beovercome in part byincreasing the copper content ofthe alloy, theincreased copper content at the bearing-backing interface inevitably isaccompanied by an increase in copper content at the bearing surfacewhere a high lead .5; content is desired.

L As a result of my investigations, I have discovered a method wherebythe aforementioned dimculties in the manufacture of copper-lead bearingsand the like may be. overcome and which 10. oiers outst-andingadvantages in the manufacture of composite bearings in general. I naccordance with my invention a porous lining of metal of relatively highmeltinglpoint is bonded to a reenforcing metal back by sintering apowder I5 of themetal in situ on the back. Thus, a layer of powdered orgranular metal (for example, a

non-ferrous metal such .as copper) is spread. or otherwise substantiallyuniformly distributed in aY substantially uncompacted condition on ametal 20 backing (for example, a ferrous alloy such as steel). Theresulting coated backing is heated to a temperature below the meltingpoint of the backing and the grammar metal but atlwhich diffusion'welding occurs, and the heating is Vcon- 25 tinued until the powderparticles or grains have been welded together toform a porous lining ormatrix and the matrix has become welded to the backing. In other Words,the uncompacted grains sinter or bond together and to the back- 30 ingand the interstices between the grains become pores. A layer of coatedmetal powder particles A(the coatings and cores of which are dissimilarand selected from the group consisting of the metal of the porous liningand a metal having 35 a substantially lower melting point)A iscompressed against the porous lining and while thus compressed is heatedto a temperature intermediate the melting points of metals of the coatedimpregnates the-porous lining. In this way there is formed a bearinglayer which is aftlxed rmly to thel backingsheet and in which theimpregnant is sufficiently well distributed to afford an excellentbearing.

Preferably, the coatings of the particles correy Fig. 1` is a schematicelevation, partly in sec- 55 ortica the form of an upright tion, ofapparatus adapted to the practice of the' invention; and

Fig.- 2 is a section through the muflle of Fig, 1,

taken alongthe line 2-2.

Referring` to the drawing, the apparatus comprises a mufile assembly Ihaving a cylindrical inner refractory heat conductive wall I I disposedin, a substantially horizontal position,. around which is wound anelectrical heating coil i2 of high resistance wlrearranged to beconnected to a current source, not shown. Around the heating coil isdisposed an annular mass I 3 of heat insulating material such asSil-O-Cel, and this in turn is enveloped by a cylindrical metal sheet I4for protection purposes. The ends of the munie are closed by a pair ofannular end pieces I5, I6, of heat insulating material which extend fromthe inner refractory wall, to beyond the metal shell. The metall shellfits in annular grooves I1, I8, cut respectively in the end pieces,which are clamped together by connectingbolts or tie rods I9, 20, 2|,22, passing through the annular mass of-insulation.

A cylindrical heat resistant'metal tube or munie 23 adapted to-slideeasily into the refractory cylinder I0 is provided for heat treatmentpurposes. The rear end of the' tube is closed by a cap 2li threaded orwelded -to said end and provided with an outlet nipple 25 welded to alower portion lthereof and a pyrometer well 26 which likewise is weldedto the c ap, extends horizontally throughout the greater portion of thetube, and is closed at its inner end. A thermocouple 21 is slidablydisposed in the well and is connected to a galvanometer' 28 ofconventional type for measuring temperature. The. fro'nt end of themunie is threaded and is provided vsviich has a concentrically disposedinlet nipple A- cylinder 3| of reducing gas under pressure, for examplevhydrogen, is connected to the inlet nipple through a reducing valve 32and av dryer sa by manso: tubing a4, as. Tne'dryer is in closed cylinder36 having an inlet nipple 31 at. the top and a side outlet nipple 38 atthe bottom and is packed with activated (i. e. dehydrated) aluminumoxide 39.

The outlet nipple 25 on the munie is connected by a tube 40 to a trap orliquid seal Incomprising a flask 4I' with a two-hole lstopper 42 43which extends into which projects a long tube below the level of liquid,preferably sulphuric acid maintained in the flask. vA short tube 44extending through the stopperfrom above the liquid level serves as anexit for gas from the system.' -d l A boat-450i' alundum or the like maybe placed -in` the muffle when the front cap is takenoif and serves tocarry the bearing strips A6, '41, 48, 49,

'50, 5I during their heat treatment.

Manufacture of copper-lead composite bearings ducted as follows:

Flatclean metal backing sheets of steel, bronze coated with a thin butsubstantiauy uniform iayer of 'dry copper powder having relatively cleansurfaces. The coated sheets on' the 'alundum boat are placed 'in thex'nullleand there heated in an atmosphere of dry hydrogen to atemperature of about 1000'C., that is -to say, to a tem- Y' vr-peraturebelw but within a hundred degrees of the melting point of copper for. a.periodo! at least one hour. During the heating period a with a screw cap29 stream of hydrogen originating in the pressure cylinder and dried bypassing through the iilter is continuously passed through the muiile andbubbles out through the liquid seal at the end of the system. Thishydrogen ser'ves to reduce any oxidation products on the surface of theparticles of copperpowder and assures that the surfaces shall be cleanand hence amenable toy diffusion welding.

Afterl the heat Vtreatment as described above, the pieces are allowed tocool in the muilie in the non-oxidizing or reducing atmospheremaintained by the hydrogen, the hydraulic seal serving to prevent theingress of air. When the pieces are cooled to about room temperature,they are withdrawn for'further treatment.

The heat treatment of the loose layer of copper powder on the backing asdescribed above results in the formation of a porous copper mixing orsponge bonded firmly -to the backing. At the temperature of treatmentdiffusion welding couples the copper particles rmly to each otherI andto the backing but leaves voids or pores.

These voi-ds may now be impregnated with molten lead or other substancescapable of giving the desired bearing surface. Thus, a layer ofcopper-,coated lead powder may be compressedv against the backing. Whilethus compressed, the' assembly is replaced in -the muilie Where it isheatedrin an atmosphere of .dry hydrogenor other non-oxidizing andpreferably reducing atmosphere to a temperature above the melting pointof lead (but below that at which the copper sponge' is melted orotherwise substantially damaged) for a considerable period of time.Under such conditions the lead melts or sweats into the porous matrix asa result of capillary attraction aided by gravity and thoroughlyimpregna-tes .the mass. Following this second heating step the mass isag'ain permitted to cool within the muie so that' it is protected fromoxidizing influences,vand' then' withdrawn. 'I'here results a laminatedsheet comprising the backing to which is welded securely a copper spongeor matrix impregnated withlead and having excellent bearingcharacteristics.

The laminated sheet may be subjected to bending; pressing, stamping orother mechanical -working to form it into a finished bearingwithlytically deposited copper powders ranging in .par-

ticle size from about 40 to about 100 mesh (Tyler scale), but finerpowders may be i employed4 if very ne pores are desired. i

Powders of metals other than copper may be employed to .form the matrix.Thus nickel-copper powder or mixtures or nickel and copper powder may beemployed. The nickel aids in bonding the matrix to the backing,particularly if it is of steel. Generally speaking, any metal having ajployed to form the matrix.

impregnation should be accomplishedI at a temperature considerablyv.below l the melting point of the matrix so that there is no danger ofdamaging the latters spongy or porous structure. In the caseof a coppermatrix, exposure to lead at 700 C.-, even though it lbe prolonged for aconsiderable period, does not damage the spongy structure substantially.As hereinbefore l indicated, impregnation may be conducted by coveringthe surface with leadcoated copper powder or copper-coated lead powder,compressing, and heating to a temperaturewhere sweating of the lead andconsequent impregnation results. I have found that by compressing aloose layer of copper-coated lead powder against the matrix and heatingthe' aggregate while maintaining the pressure, sweating of lead occurswhen the layer is heated to a temperature of 750 C. in contact withaporous copper matrix for a period of about an hour so that thecopper-coated lead particles become firmly anchored thereto and to eachother and form an excellent bearing surface. For example,

when a loose layer of copper-coated lead particles containing as littleas 12.5%' lead is pressed againsta porous copper matrix (formed asdescribed hereinbefore on a. backing sheet) and while thus pressed ismaintained at 750 C. in a reducing 'atmosphere for a period of one houror more, the lead sweats and impregnates the ma-A trixwithout damagingit. With higher proportions of lead in the powder the temperature ofimpregnation may be considerably lower andv approaches the melting pointof lead.

Treatment of the porous matrix by heating a mass of fine copper-coatedlead particles in contact therewith to a temperature above the meltingpoint of lead and while subjecting the mass to compression so as tosqueeze molten lead out o-f the particles and cause it to enter andimpregnate the matrix, as described hereinbefore, is a desirable aspectof my invention in that it permits a close control of the distributionand proportionof lead and copper at the bearing surface irrespective ofthe size and proportion of pores in the matrix. BY employing very finecoppercoated lead powder in this manner the distribution of copper andlead at the bearing surface becomes very uniform and segregation of leadis inhibited. By varying the proportions of lead to copper in the powderthe proportions of these two metals at the bearing surface canbe'controlled. The copper coatings on the particles tend to weldtogether and to the matrix and form an addition thereto, while the leadpenetrates throughout the whole bearing layer. y v

Lead alloys and other metals or-alloys of relatively low melting pointmay be employed as impregnants for the matrix. Thus hard lead alloyscontaining appreciable quantities of antimony, etc., may be used.

Unless metal powders with absolutely unoxidized surfaces are available,and this is seldom the case in practice, heat treatment in areducvsisting of the metal of the porous lining and a ing atmosphere isessential. Other reducing gases, such as those obtained by crackingarnmonia, may be employed instead of hydrogen.

In any case, the presence of water vapor should be avoided insofar aspossible-during Aheat treatment, and I have found a dessicator ('of thetype illustrated in the drawing) containing activated alumina to besatisfactory. Periodically such a dessicator should .be revivied byremoving it from service and blowing air through it while hot.

' The matrix maybe formed advantageously on' a rough electricallydeposited metal surface, for example, the rough surface which obtainsupon a copper cathode. Such a surface offers an admirable base for thebearing.

I claim:

1. A methodof making a composite bearing which comprises placingpowdered substantially solid copper on a metal back to form asubstantially uncompacted coating, heating the back thus coated to atemperature below the melting point of copper but within Va hundreddegrees centigrade thereof until the copper powder particles bond toeach other. and to the backing to form a porous matrix welded to thebacking,

, compressing a layer of copper-coated lead powder against the porousmatrix vand While thus compressed heating it to a temperatureintermediate the melting point of copper and of lead until the leadsweats and impregnates the matrix.

2. A method of making a, composite bearing which comprises forming aporous lining of metal of relatively high melting point bonded to areinforcing metal back by sintering a powder of the metal in situ on theback, compressing against the porous lining a layer of coated metalpowderparticles, the coatings and cores of which are dissimilar andselected from the group conmetal having a substantially lower meltingpoint, and while thus compressed heating the layer to Aa temperatureintermediate the melting points of metals of the coated powders untilthe-metal of lower melting point impregnates the porous lining. s

3. A method of making a composite bearing which comprises forming aporous lining of metal of relatively high melting point bonded to areinforcing metal back by sintering a mass of powder of the metal insituon the back, compressing a layer of coated metal powder particlesagainst the lining, 'the coatings of the particles corresponding to themetal of the liningand the cores of the particles being of metal ofsubstantially lower melting point, and while thus compressed heating thelayer to a temperature intermediatel the melting points of the metals ofthe cores and coatings until the metal of the cores sweats andimpregnates the porous lining.

ERICH FEIZ.

